Carboxylated emulsion polymers such as Sinclair-Koppers K-55E latex have been known since the early 1950's. Such latices had enhanced chemical and mechanical stability. Additionally, such polymers provide improved binding power as they are self crosslinking.
While the polymers per se are extremely useful, they have had to be prepared under acidic conditions. This necessitated using glass lined or stainless steel reactors.
Since the early 1970's polymer chemists and process engineers have been seeking ways to produce carboxylated polymers at alkaline pH's.
One of the early attempts in this area is disclosed in Hoechst's Belgium Patent 766,365 published Apr. 27, 1971. This patent discloses polymerizing a styrene butadiene monomer mixture to 75-97% conversion at alkaline pH then adding a mixture of unsaturated acid and styrene and continuing the polymerization to complete conversion. Various other attempts have been made to sequence the polymerization so that the acid is incorporated over a relatively short period of time. Most of these procedures have not met with extensive commercial application. One of the problems is that it is still necessary to carry out at least a portion of the polymerization at acid pH's.
U.S. Patent 4,065,423 issued Dec. 27, 1977 in the name of Uhiroyal Inc. discloses polymers containing acryloyloxy carboxylic acid monomers. This patent also teaches that the emulsion polymerization must be carried out at a pH from 1.5 to 7.0 preferably from 3 to about 5 (col. 4, lines 34-35).
Applicant discovered that acryloyloxy carboxylic acid type monomers may be polymerized at pH's in excess of 7.5, preferably in the range of 8-11. The polymerization need not be conducted in glass lined or stainless steel reactors.